The subject invention relates to electrical apparatus, such as transformers and capacitors, designed to use as a liquid dielectric fluid polychlorinated byphenyls, and a porous internal construction. Such apparatus is characterized by the adsorption of the liquid into the pores of structural support media, thereby rendering difficult the complete removal of said liquid.
For many years polychlorinated biphenyls (PCB or PCB's) have been used as an insulation or dielectric fluid in the electrical apparatus industry as a safe, fire resistant material. Dielectric fluids containing such PCB's have often been generically called askarels where the PCB is often present as a mixture in a chlorinated benzene solvent. In the late 60's and early 70's it was discovered that PCB's were hazardous environmental contaminants and their use was discontinued; however, by that time many pieces of electrical apparatus had been built using the PCB's as an insulation media. A primary use of PCB is in electrical transformers and electrical capacitors as a coolant dielectric fluid. This invention relates to cleaning PCB's from such apparatus and eventual reclassification of it as non-PCB equipment. For reclassification it is presently necessary that tests demonstrate a contamination of less than 50 ppm of PCB in the dielectric fluid after three months of operation succeeding the completion of cleaning.
Transformers designed for PCB use all have a major similarity in that they contain a cellulosic material as insulation, usually a paper wrap, on the wire comprising the core of the transformer. Included in the transformer may be wooden structures acting as insulators. Because of these two major items, the interior of the transformer acts somewhat like a sponge and PCB's become impregnated into these materials. They are contained in such a manner that simple washing will not remove them, and that, over a period of time, the PCB's will leach out of the cellulosic material and come to an equilibrium level in the transformer even if it had been filled with clean, non-PCB, oil. Transformers which use a mineral oil dielectric are different and the invention does not apply.
A similar problem is encountered in the disposal of transformers and capacitors which are impregnated with more than 500 ppm PCB or PCB contaminated liquids which are understood to be liquids containing from 50 to 500 ppm PCB. Regulations imposed by the United States Environmental Protection Agency prohibit the recovery and recycling of the equipment unless the equipment can be certified as non-PCB equipment under those regulations.
Several methods are used or have been proposed for the cleanup, or reclassification, of transformers. Complete flushings have been proposed with several classes of fluids thereby generating large volumes of PCB contaminated, or PCB, material by the United States Environmental Protection Agency (EPA) definitions. These methods involve vacuum extraction and condensation of vaporized solvents but have been found lacking for a number of reasons.
The major problem with prior methods is that they either generate a very large volume of contaminated fluid, with more than 500 ppm of PCB, and require long periods of time to successfully complete cleaning or they include complicated process steps during which the equipment must be kept out of service or service is frequently interrupted. Several discussions of the problem of cleaning PCB and PCB contaminated electrical apparatus, particularly transformers, are found in U.S. Pat. Nos. 4,483,717, 4,425,949 and 4,312,794 and a literature reference ("Transformer Askarel Removal to an EPA Clean Level," J. H. Olmstead. Proceedings IEEE, 1 AS 79:34, See pages 1053 through 1055), which describe the cycling of transformer dielectric fluid through a filtration system to scavenge PCB.
Other methods suffer from high labor requirements, the necessity of hauling of contaminated fluids to separation equipment, often over public roads to offsite locations, or employ complicated separation techniques. Up to now simple, onsite and unattended apparatus and methods for cleaning, or reclassifying, transformers designed for PCB dielectric fluid while maintaining the transformer on line and energized, or under a power load, having been wanting. With this invention such problems have been solved.
Also provided as a part of the present invention is a cleaning system (apparatus) for use in the practice of the present method.